1. Field of the Invention
The present invention relates to an electromagnetic noise absorbing material and an electromagnetic noise filter, and to a manufacturing apparatus and method for a tape-shaped electromagnetic noise absorbing material.
2. Background Art
Recently, in concert with the spread of high-speed digital devices, the phenomenon in which unwanted electromagnetic waves generated by such devices cause interference with other devices (the electromagnetic compatibility problem, known as the EMC problem) has become a new environmental problem. For example, unwanted electromagnetic waves within a range of 30-1000 MHz generated when common mode noise current is placed on cables of a digital communication apparatus causes interference with respect to televisions and the like, and this is seen as a problem.
Conventionally, electromagnetic noise filters were employed which used magnetic substances as electromagnetic noise absorbing materials.
The relative magnetic permeability .mu..sub.r (f) of a magnetic substance is obtained by the following formula. EQU .mu..sub.r (f)=.mu..sub.r '(f)-j..mu..sub.r "(f) (1)
Here, .mu..sup.r ' represents the effective relative magnetic permeability, .mu..sub.r " corresponds to the loss, j equals (-1).sup.1/2, and f represents the frequency.
Elect romagnetic noise filters employing magnetic substances make use of electromagnetic noise suppression effects resulting from the loss of the magnetic substance; it is necessary that the impedance and resistance with respect to electromagnetic noise be large. Accordingly, it is necessary that .vertline..mu..sub.r .vertline., the absolute value of .mu..sub.r, and .mu..sub.r " be large, and that .mu..sub.r " be greater than .mu..sub.r ', in such electromagneti c noise absorbing m aterials.
Frequency characteristics of a representative relative magnetic permeability (.mu..sub.r '(0)=1500) in ferrite magnetic substances, which were conventionally used as electromagnetic noise absorbing materials, are shown in FIG. 37 (Junnosuke Kamitoono: "Denji Kankyoti Kougaku Jyouhou", page 152, Jun. 30, 1992, Special Issue, Mimatsu Data Systems). Between the relative magnetic permeability .mu..sub.r '(0) of the ferrite magnetic substance and the upper limit frequency f.sub.c (f.sub.c is defined as the frequency at which .mu..sub.r " exhibits a peak), the following limit law holds: EQU .mu..sub.r '(0).times.f.sub.c =5.6 GHz (2);
in ferrite, this is due to the use of magnetic resonance loss as magnetic loss (Soushin Chikazumi: "Jiseitai no Butsuri (second half)", page 325, Shokabou, Mar. 20, 1984). The dotted line in FIG. 37 indicates the limit line of Formula (2). This indicates that in Formula (2), in the case in which the frequency characteristics of the ferrite magnetic substance are set so that .mu..sub.r " becomes larger within a specified frequency band, the values of .vertline..mu..sub.r .vertline. and .mu..sub.r " are uniquely determined. The frequency characteristics of the relative magnetic permeability in a Mn--Zn ferrite, comprising a representative ferrite magnetic substance, are shown in FIG. 38. The condition .mu..sub.r "&gt;.mu..sub.r ' is met at a level of a few MHz or more; however, the absolute value of .mu..sub.r is only this small value. In this case, in order to increase the electromagnetic noise absorbing effect, there is no other method than to increase the volume, and accordingly, it is necessary to use large amounts of the electromagnetic noise absorbing material, and this creates a problem in that the product size becomes large.
Furthermore, as shown in FIGS. 37 and 38, the relative magnetic permeability of the ferrite magnetic substance has an extremely small value in the high frequency band, so that the effects as an electromagnetic noise absorbing material decrease drastically at a level of a few hundred MHz or more. That is to say, there are defects in that the electromagnetic noise suppression effect is small with conventional electromagnetic noise absorbing materials, and the electromagnetic noise suppression effect declines dramatically at levels of a few hundred MHz or more.
Examples of the conventional electromagnetic noise filter employing the electromagnetic noise absorbing material (ferrite magnetic substance) described above include the ferrite core 901 shown in FIG. 39, which was conventionally employed. The size thereof is such that, for example, d=10 mm, t=4 mm, and 1=30 mm. As shown in FIG. 40, this is installed on a cable 902. The electromagnetic noise filter must have a large impedance and resistance, and a level within a range of from a few tens to 100 .OMEGA. at 30-1000 SHz is necessary. The frequency characteristics of the impedance (Z=R+j.multidot.X) in the ferrite core are shown in FIG. 41. Here, Z indicates the impedance, R indicates the resistance, x indicates reactance, and j indicates (-1).sup.1/2. At 30-1000 MHz, Z and R have values within a range of from a few tens to 200 .OMEGA., and thus meet the above conditions; however, the ferrite core has a large volume and weight in comparison with other electrical parts, and when this is loaded, the flexibility of the cable is lost. Furthermore, the impedance is reduced at levels of a few hundred MHz or more, so that such an electromagnetic noise filter is not effective with respect to electromagnetic noise of a few hundred MHz or more.
Another example of an electromagnetic noise filter employing a conventional electromagnetic noise absorbing material (ferrite magnetic substance) is the ferrite bead shown in FIG. 42. For example, the size thereof is such that r=0.65 mm, tm=1.1 mm, and 1=5.0 mm, and .mu..sub.r '(0)=1500. The electrical circuits and the conductor of the cable are passed through the interior of this cylinder. The frequency characteristics of the impedance in this case are shown in FIG. 43 (Junnosuke Kamitoono: "Denji Kankyou Kougaku Jyouhou", page 152, Jun. 30, 1992, Special Issue, Mimatsu Data Systems).
A value of a few tens of .OMEGA. is exhibited at 30-1000 MHz; however, in the electrical circuitry, in comparison with other electrical parts, the sizes of the parts are quite large. In this way, the conventional electromagnetic noise filters (ferrite cores, ferrite beads) possess problems in that the part size was large, the flexibility of the cable was lost, and such electromagnetic noise filters were ineffective with respect to electromagnetic noise at a level of a few hundred MHz or more.
Furthermore, FIG. 44 shows a conventional cable (for example, having a diameter of 10 mm and 24 wires); for example, cables are passed through the interior of the cylinders of the ferrite cores. In the Figure, reference numeral 903 indicates a conductor, reference numeral 904 indicates an insulator, reference numeral 905 indicates a shield material, and reference numeral 906 indicates an insulator. Conventional cables do not possess an electromagnetic noise suppression function, and furthermore, as a result of the combination of a conventional cable and an electromagnetic noise filter (ferrite core), the volume and weight of the part become large, and the flexibility of the cable is lost.
FIG. 45 shows a thin film manufacturing apparatus which was conventionally used for manufacturing a metal magnetic tape for magnetic recording media. This apparatus comprises raw material source 907, feed bobbin 908, winding bobbin 909, guide axles 910, and cylindrical can 911. A non-magnetic insulator tape substrate 912 is sent from feed bobbin 908 to winding bobbin 909, along guide axles 910 and cylindrical can 911, and a magnetic film is deposited on the non-magnetic insulator tape substrate 912 in a vacuum. Magnetic recording media do not require that uni-axial magnetic anisotropy within the film surface of, in particular, the magnetic film, be present, so that during the deposition of the magnetic film, an external magnetic field was not applied in a direction within the film surface of the magnetic film. Furthermore, for this reason, the thin film manufacturing apparatus was not provided with a mechanism for applying an external magnetic field in a direction within the film surface of the magnetic film, during the deposition of the magnetic film.